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For Safety's Sake, It Is Essential To Leave Engineering Design To Engineers

Burgess COMMENTARY

Peter Burgess

For Safety's Sake, It Is Essential To Leave Engineering Design To Engineers

In 2008 I was involved in a detailed design of an expansion of a facility in Bohai Bay. I had worked on the detailed design of the original facility in 2001/2. The facility was installed and commissioned in 2002/3. In 2008 I was sent to the facility to help the operators run a system they had trouble with for the previous 5 years since commissioning the plant in 2003. See my blog entitled 'Who Should be Involved When Writing Operating and Commissioning Procedures?'

During the design phase of the expansion in 2008, when I was getting up to speed on the new equipment to be added, I was horrified to see the existing system. Because it was designed 5 years earlier and I had not remembered the finer details, I looked at the existing system thinking I had designed it. When I saw it, I almost fainted. I had it in my mind that the least I should do was to request the institute of chemical engineers to revoke my membership and chartered status, hopefully forgive me, modify the existing design so that it was safe and then send me to a remote island in the Pacific and never let me near another design office again. This was the best outcome for me that I could think of. These were the thoughts that went through my head when I saw the as built P&IDs of the existing process. The reason I was so horrified was because the inlet heat exchangers (2 off) and their inlet piping could be overpressurised from the wells simply by closing one of many isolation valves.

This would have subjected the class 150# system to high pressure from the class 600# production manifolds fed by the API 5000# wellheads with no protection apart from high pressure instruments (no relief protection). When I saw this design it ran contrary to my normal design practices. It was just a matter of time before someone made a mistake and closed the wrong valve. I had visions of the platforms blowing up and operators diving into the waters of Bohai Bay and me in a Chinese Court being found guilty of negligence and sentenced to death. In China, they don’t have a death row like they do in the US where a convicted person can spend decades waiting for their execution. In China it takes less than an hour after sentencing and you get a bullet in the back of the head outside the courthouse. Hence I was also booking flights out of the country.

The first thing I did was request a set of original Phase 1 drawings, the actual P&IDs I and my team prepared five years earlier. I was forlornly hoping that the original design had actually been OK and maybe some modifications had been made since then that were not my doing. These were sent to me a few days later (after the same number of sleepless nights) and when I received them, I have never breathed a bigger sigh of relief. In the original design there was only one heat exchanger to heat the process fluids, not two and we had included an interlocking system of valves that meant there was always a flow path open to the relief valves on the Production Separator. On further investigation, the second heat exchanger had been added by operations department without recourse to engineering and they had destroyed the system’s safety integrity in doing so as they had added a lot of isolations that now rendered the system unsafe. To put this in perspective, a temporary plant modification was once done on a previous plant, a cyclohexane plant in Britain called Flixborough. I am ashamed to say that proper design procedures had not been followed in that particular plant and it was apparently a decision by the managers who were chemical engineers like me and should have known better. Never ever bypass engineering no matter how confident you are and no matter how small the job!!!

The Flixborough plant modification failed and 28 people were killed and many more seriously injured not to mention the devastation to the local community housing for miles around. I have 40 years experience and am good at design but I would not bypass the standard engineering procedures.

The FEED team for the expansion project had justified the design by taking advantage of an API-14C clause that said that if a fully independent pressure shutdown system was installed, then a PSV may not be necessary provided that the system dynamics are such that the shutdown valve closure is fast enough to avoid overpressuring the downstream system. As far as I knew no dynamic simulation of the system had been done. Even if it was done and found to be satisfactory, it would be hard to trust this given the state of the instrumentation that I observed whilst on the platform. API-14C advises caution if this clause is used. I would go further and say that this constitutes a HIPP system and as such would have to have all of the attributes of a HIPP system. It did not. I added full flow PSVs to resolve this (so I could sleep easily at night). The original flare system design was done to cater for this and as such it was the best solution.

Later that year while I was at the offshore facility working on the heat medium system, I discovered a number of other things wrong with the design. The extra heat exchanger had been added presumably in an attempt to get more heat into the system. At least while I was on the platform, both exchangers were operating. However, all that had been done was to add the second exchanger in parallel without redesigning the heat medium piping and control system. These were left as they had been designed originally. Hence the system was bottlenecked by the piping and temperature control valve. The design pressure and temperature had also been specified at 30 barg at 200°C compared to the original 31 barg at 232 °C. Hence the system design integrity had been decreased and really could only safely operate at a temperature of around 190°C max compared to the original design of 208°C. Another part of the system, the waste water treatment plant was not performing. It was bottlenecked on the drains. This meant the hydrocyclones were operating at a dP ratio of 1. Hence the hydrocyclones were doing nothing. The 3” drain should have been replaced with a 4” or preferably a 6” drain to fix the problem. A few years later I heard they were demolishing the whole waste water system to install a world first multi stage (in one vessel) compact flotation unit. I also heard they had trouble with it. When I made recommendations in my report on the platform trip, I had recommended they employ someone to look at these systems to see what could be done to fix it (someone like me), but they never invited me to join them.

In conclusion, for safety’s sake and for a properly designed plant that will perform at a premium, it is essential for producers to ensure that proper procedures are followed in design and to ensure this, every plant modification no matter how small must go through engineering.